Alterations in Circulating Thyroid Hormones and Thyrotropin after Complete Thyroidectomy

Publisher Website
Google Scholar
Abstract
Changes in serum TSH, T4, T3, and rT3 concentrations after complete thyroidectomy were observed in 21 euthyroid patients with thyroid carcinoma. Serum TSH levels rose progressively during the 4 weeks of observation and a significant increase was noticed as early as 54 h after thyroidectomy. Serum T4 and T3 concentrations decreased significantly 42 and 6 h, respectively, after thyroidectomy. However, serum rT3 levels increased significantly within 18 h and reached maximum levels 30 h after thyroidectomy. The rates of decrease of serum T4 and T3 concentrations were constant between the 6–28 days after thyroidectomy (t)/2, 16.3 and 22.3 days, respectively), and the decrease rate of serum rT3 levels was similar to that of serum T4 after the day 18 (t1/2, 16.6 days). An initial sharp decrease in serum T3 and a sharp increase in serum rT3 concentrations without a significant change in serum T4 concentrations seems to be due to inhibition of outer ring monodeiodination in postsurgical states. When a significant increase in serum TSH levels was noticed 54 h after operation, both serum T4 and T3 levels were significantly lower than initial levels. The rates of fall of serum T4, T3, and rT3 concentrations were much slower than the corresponding values for labeled hormones. The slow rate of decrease of serum T3 or serum rT3 is due to monodeiodination of T4 in peripheral tissues; the slow rate of decrease of serum T4 may be due either to the decrease in T4 disposal rate in hypothyroidism or to the release of T4 from peripheral tissues to serum as serum T4 concentrations decrease.